374 CA. Young on a new method 
termine the instant of contact by noticing the extinction of the 
bright needle. 
Similar remarks apply to F, or any other line of the chromo- 
puted point of contact across the center of the slit, I had the 
unspeakable gratification of seeing everything take place as ex- 
ected. First, a full half minute before the time of contact, 
the sharp point of the needle was truncated by the dark edge 
of the moon, then it grew steadily shorter, (not less brilliant 
what remained of it) until finally its last spark vanished, the C 
line became exactly like its neighbors, and the contact was ef- 
ected. 
The observation was as easy and definite as that of the tran- 
sit of a moderately slow star, @ Ursee Minoris for instance. I 
am confident the observation may be relied upon within a frac- 
tion of a second, although it was from 5 to 15 seconds earlier 
than the time assigned by any of the other observers, I am 
informed by Professor Mayer, however, who had charge of the 
photographic operations of our party that it agrees within one 
third of a second with the time deduced from a preliminary 
measurement of a photograph taken about 15 seconds after the 
contact was announced, ‘ 
ith an instrument of sufficient dispersive power, the slit 
might be opened somewhat widely, and placed tangent to the 
sun’s limb. In this case a slight error in the estimated point 
of contact would not interfere with the accuracy of the obser- 
vation 
I wish to call attention to the applicability of this method 
at the coming transits of Venus. It is not possible, perhaps, to 
predict just how great will be the effect of her atmosphere ; bu 
it is difficult to see in what respects this method will suffer from 
it more than any other. It certainly presents this great advan- 
tage, that the observer will perceive and watch the planet's ap- 
proach long before the instant to be observed, and thus have all 
the benefit of preparation. : 
It seems likely also that the instant of internal contact will 
be more easily seized with the spectroscope than with any other 
instrument. Instead of the rupture of a black ligament, It 
ought to show the sudden formation of a brilliant line running 
the whole length of a before dusky spectrum, a phenomenon 
much more striking than the other. 
While the moon was advancing upon the sun, special atten- 
tion was paid to the appearance of the um lines near her 
limb, They came up to the edge perfectly square and straight, 
even when the limb made an angle of only 5° or 6° with the 
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